This invention relates to a gear shift control apparatus for use with an automatic transmission having friction elements, such as clutches, brakes and servos, pressurized and vented to cause the transmission gear ratio to change.
For example, Japanese Patent Kokai No. 5-157168 discloses a gear shift control apparatus adapted to produce a change from the current gear ratio to a desired gear ratio by increasing the pressure of the working fluid to a first friction element to engage the first friction element while decreasing the pressure of the working fluid to a second friction element, inversely to the working fluid pressure increase, to release the second friction element. If the first and second friction elements are subject to different friction factor changes, however, the engagement of the first friction element will be advanced or retarded with respect to the disengagement of the second friction element, causing a great torque reduction or engine racing during the torque phase.